Last Friday afternoon, The Financial Times released an expansive report accusing Thomas Piketty of doing shoddy analysis of data on wealth inequality for his best-selling book, "Capital in the Twenty-First Century." In the six days since, economists and writers around the world have produced many thousands of words on the controversy. Outsiders have weighed in on the newspaper's case, the newspaper responded, and Mr. Piketty, on Thursday, provided his first detailed defense.

So where do things stand? How much do the criticisms by The Financial Times hold up, and should "Capital" continue to be viewed, as many reviewers have argued, as a definitive volume on inequality of income and wealth in advanced nations?

Here, we review the claims and counterclaims and conclusions one can draw about L'Affaire Piketty.

Who is Thomas Piketty, and why should anyone care about this book?

He is a French economist who has done groundbreaking work parsing old tax data and other historical records to try to discern the (very) long-term trends around inequality of wealth and income. He and other scholars, notably his frequent collaborator Emmanuel Saez, have helped answer questions that society previously had few good answers to. Namely, how much of the wealth in various advanced nations has been held by the top 1 percent at various times in history?

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Thomas Piketty in his office at the French School for Advanced Studies in the Social Sciences.CreditCharles Platiau/Reuters

The book's argument in a nutshell is this: Capitalism has a natural drift toward high inequality, as assets like real estate and stocks disproportionately held by the wealthy (capital) rise faster than the economy (growth). This process was temporarily reversed by the world wars of the first half of the 20th century, but now inequality in the United States and Europe is rising back toward pre-World War I levels. This is a bad thing, which should be fought through radical policy measures like a global tax on wealth.

In "Capital in the Twenty-First Century," published in the United States in March (and in France last year) Mr. Piketty combined that data work with some literary criticism, philosophy, theory and prognostication for a sweeping look at the past, present and his expected future of inequality of wealth and income. It has been on the New York Times best-seller list for six weeks, including three in the No. 1 spot. This is not common for a book about economics, and this one happens to be 696 pages.

One thread that has run through many reviews has been praise for Mr. Piketty's work with historical data, paired with disagreement concerning some of his conclusions about what it all means for the future. Mr. Piketty's reputation for careful analytical work has increased the authority of his broader conclusions and policy recommendations. So he would have much to lose if a consensus developed that his analytical work was shoddy.

What is in dispute?

Plenty of people have taken issue with Mr. Piketty's more philosophical and predictive conclusions. But last Friday, The Financial Times published a collection of articles by its economics editor, Chris Giles, accusing him of flawed and sloppy techniques for analyzing historical data. (The Financial Times's critiques are summarized here and described at length by the newspaper here).

Some of its critiques centered on what the newspaper characterized as mistakes and modifications to data that appear arbitrary and without consistent justification — but do not undermine the core findings of his work.

A response from Mr. Piketty, published on his website on Thursday, said that these were not in fact mistakes, but choices he made to try to make the data more accurate, and which were cataloged (along with his reasons for making them) in technical notes accompanying his data.

Another line of criticism is that Mr. Piketty cherry-picked a source of data for British inequality that gave a distorted picture of the trend there in recent decades. The data source Mr. Giles argues would be more reliable paints a very different picture, indicating that the share of wealth held by the top 1 percent in Britain is 44 percent, not 71 percent, and has been flat in recent decades.

Mr. Giles takes issue with Mr. Piketty's use of estate tax data from British authorities, writing that the authorities producing that data explicitly say it is best not used for purposes of comparing wealth trends over time. He argues instead for a survey of wealth in Britain, which he concludes is more reliable evidence.

If the data Mr. Piketty relies on for Britain is indeed deeply flawed — and Mr. Giles's preferred approach more accurate — it would undermine Mr. Piketty's broader argument.

It is on that basis that The Financial Times states "there is little evidence in Prof Piketty's original sources to bear out the thesis that an increasing share of total wealth is held by the richest few."

Mr. Piketty acknowledges that the data he used to measure British inequality, from estate tax returns, is imperfect. But he says that using Mr. Giles's preferred data source isn't a good way to go, because it is not comparable to data from earlier periods. The data for decades past are based on estate tax data, not surveys. Moreover, he notes that other research using different methods has also pointed to rising inequality in Britain in recent decades, making the result from Mr. Giles's approach inconsistent with other evidence.

What can we be comfortable in concluding about wealth inequality?

The evidence for one of Mr. Piketty's key points is overwhelming: Income inequality has risen significantly in the last few decades in both the United States and Europe. Data on the concentration of wealth is less reliable, and that is the crux of the dispute. Even with wealth, though, we can be reasonably confident that it is becoming more concentrated in the hands of the top 1 percent in three of the four countries Mr. Piketty studies most closely (the United States, Sweden and France). It is British wealth inequality that is in dispute.

Has Mr. Piketty acknowledged any errors?

Not really. Mr. Piketty concedes no outright errors in his original work, though he acknowledges that many of his choices can and should be subject to debate and are worth refining further.

And he says he could have done a better job disclosing his methods and reasons for data adjustments. For example, in addressing one piece of early 20th-century Swedish inequality data that Mr. Giles argued was in error, Mr. Piketty wrote, "I agree that this adjustment should have been made more explicit in the technical appendix and Excel file."

What broader lessons can be drawn from this controversy about the nature of social science, historical research and the search for truth?

Quite a few! But this is the biggest one: The work by Mr. Piketty and others trying to study economic history is challenging for a lot of reasons, not least that good economic data is generally unavailable for anything more than the most recent few decades. So researchers must use whatever sources available, frequently old tax filings, to try to come up with some estimate of how things were in an earlier era.

The problem is, to make that data useful — and particularly to make it comparable to more recent data that is collected in a rigorous and transparent way — scholars have to make hundreds of adjustments to account for various factors that could throw off the numbers. To cite one of many adjustments that was at issue in the recent controversy: If you want to know what the level of wealth inequality was in 1930s France based on estate tax data, you must use some mechanism to deal with the fact that the people paying the estate tax are, well, dead, and probably don't precisely line up with the wealth trends of all people who were alive at the time.

Because scholars must make countless assumptions to find useful data, there are countless opportunities for either conceptual error or willful manipulation. In that sense, the casual reader is trusting the researcher to make those judgments in a consistent, logical way that is not intended to tilt the data one way or another.

Any other points?

Maybe that people doing heavy-duty social science might consider using programming languages that allow more clearly disclosed and notated series of steps that outside researchers can more easily check and second-guess, instead of Microsoft Excel or other simple spreadsheets. Here's our own Austin Frakt arguing just that. That said, Mr. Frakt notes that Mr. Piketty's analysis is ultimately relatively simple mathematically, and so using simple spreadsheets — and then opening them up for the world to see and second-guess — may have been the best way to go.

Is this debate over?

We hope so. The Financial Times vs. Piketty back-and-forth began last Friday afternoon, and now has spanned about a dozen separate articles, posts and ripostes. That doesn't even count the commentary on their dispute around the Internet (including here at The Upshot). The point of diminishing marginal returns of further debate around these relatively narrow issues seems to have set in.

So who won? Is "Capital" a reliable guide to the past, present and future of global inequality, or is it a schlocky polemic based on cherry-picked data?

If we had to summarize the consensus that has emerged on L'Affaire Piketty, it goes something like this. Mr. Giles raised worthwhile issues about Mr. Piketty's methods that are fair to debate. But Mr. Piketty's response also makes clear that Mr. Giles's approach has flaws of its own and shows less inequality in Britain than there actually is.

Indeed, Mr. Giles's results point to a world at odds not just with Mr. Piketty's data, but also with that by other scholars and with the intuition of anyone who has seen what townhouses in the Mayfair neighborhood of London are selling for these days. That doesn't mean Mr. Giles is wrong — the whole point of academic research is to gain something more solid than intuition — but the idea that the whole of Mr. Piketty's argument rests on a few shaky assumptions seems unfair to the Frenchman.

Her poetry of self inspired the oppressed across the world to believe that they could reveal their personal experience.

A brilliant writer, a fierce friend and a truly phenomenal woman.”

So said US President Barack Obama of Maya Angelou, leading tributes from around the world after the news was posted by her family on Facebook that she had died at the age of 86. In 2011, Obama presented her with the Presidential Medal of Freedom, the highest award for a civilian in the United States. As he said at the time, she was many things – author, poet, playwright, actress, director and composer – but “most of all, she was a storyteller – and her greatest stories were true”.

Angelou is a great American writer, studied in schools and universities across the country and hailed by politicians – former US President Bill Clinton said that she was a “national treasure” and he and former US Secretary of State Hillary Clinton had lost a “beloved friend”. Hers was an American story: Rags to riches, overcoming prejudice and misfortune to touch the American dream. But her impact was worldwide; she was more than a national writer. Her poetry and stories were translated into dozens of languages. She taught the world about the power of language – and how words could change the world.

Where she had the greatest impact was her autobiographical fiction. Her blend of memoir, autobiography and fiction created incredible, powerful stories – and opened up the potential of the intimate, no-holds-barred memoir to readers and writers across the world.

Feted and influential

For the young Marguerite Johnson to become so feted and influential would seem impossible. She was born to a nurse and navy dietician in St Louis, Missouri in April 1928 – a second child in a disastrous marriage. At four, she was sent to live with her grandmother in Arkansas, along with her brother. He called her “Maya”, while trying to say her name – and it stuck.

While staying with her mother at the age of seven, she was sexually abused and raped by her mother’s boyfriend. The rapist was imprisoned briefly by the authorities – and killed when he came out. Maya was struck dumb by the experience. As she said, “I thought my voice had killed a man and so it wasn’t safe to speak.”

For the next five years, she was silent – choosing to be mute, as she put it. She poured all her energy into reading, devouring books enthusiastically whenever she had a spare moment. Finally, a friend of her grandmother’s persuaded her to speak – telling her that poetry could only be truly understood when read aloud.

Angelou moved to San Francisco to live with her mother when she was 14. In the years that followed, she had a son at 17 and went deep into the city’s nightlife as a dancer, singer and brothel madam.

She moved to New York and became active in the Civil Rights Movement. Devastated by the assassination of Martin Luther King in 1968, she began trying to write her life from the age of three to 17, with encouragement from the author James Baldwin. The book was published as I Know Why the Caged Bird Sings.

When I Know Why the Caged Bird Sings burst into the literary scene in 1969, its raw honesty and incredible intimacy was shocking.

The revelations about girlhood, family abuse and poverty made it a bestseller, spending two years on the New York Times bestseller list. At the same time, she challenged the form of the autobiography, using techniques of dialogue, scene setting and plot development usually associated with fiction.

An inspiration for writers of autobiography and fiction alike, I Know Why the Caged Bird Sings also showed that the most personal experience could have a huge political ramifications. It opened up new possibilities for black women writers to explore subjugation and marginalisation – and pointed new directions for African-American and black writing by women and men. Thanks to the book, the stories of the young and oppressed would never be overlooked or ignored again.

In 1993, Bill Clinton chose Angelou to recite her poem, On the Pulse of Morning at his inauguration. In the weeks after, sales of her books rose 500 percent across the world – and one reviewer called her the “black women’s laureate”.

Her poetry was a revelation

To writers, particularly women in Africa and those struggling under oppression, her poetry was a revelation; in contrast to complicated words and imagery fashionable in many western poems, she combined straightforward and powerful images to expose the pains and joys of her experiences. Thanks to her, the poetry of self became newly important – and the oppressed across the world were emboldened to believe that they could reveal their personal experience.

Many found Angelou’s work hard to stomach – the American Library Association listed I Know Why the Caged Bird Sings as one of their top 10 books most likely to be banned from high school classrooms. But nearly 50 years on, it is rated by many writers as the most influential memoir of the 20th century.

Angelou went on to write six more books of memoir, three volumes of poetry, essays and books of poetry, as well as television and film scripts and two cookery books. Her last volume of autobiography, Mom & Me & Mom came out in 2013.

Even at the end, earlier this week, she was busy writing a new book – and tweeting. In a world where many still suffer from discrimination, prejudice and children are still exploited by adults, her work speaks to millions. Her last tweet from @DrMayaAngelou was: “Listen to yourself and in that quietude, you might hear the words of God.”